1. Field of the Invention
The invention relates to paper machine clothing and especially to the fabrication of forming wires which may be used on papermaking machines. More particularly, it relates to such fabrics made from monofilaments of synthetic polymer resins.
2. Brief Description of the Prior Art
Papermaking machines are well known in the art. The modern papermaking machine is in essence a device for removing water from the paper furnish. The water is removed sequentially in three stages or sections of the machine. In the first or forming section, the furnish is deposited on a moving forming wire and water is drained through the wire to leave a paper sheet or web having a solids content of circa 18 to 25 percent by weight. The formed web is carried into a wet press felt section and passed through one or more nip presses on a moving press felt to remove sufficient water to form a sheet having a solids content of 36 to 50 percent by weight. This sheet is transferred to the dryer section of the papermaking machine where dryer felts press the paper sheet against hot steam heated cylinders to obtain a 92 to 96 percent solids content.
On papermaking machines, endless belts are employed in the various sections to carry the sheet or web of paper. There are a wide variety of forms of the endless belts, some fabricated from metal and others from textile material such as cotton, cotton and asbestos, asbestos and synthetic fibrous or filamentous materials. The selection of a given material is dependent to some degree upon the use to which the fabric will be put, i.e. as a forming fabric, dryer felt, etc.
One form of belt which has been used extensively as a forming wire in the forming section of the papermaking machine is one fabricated from an open weave of synthetic, polymeric resin monofilaments. Such fabrics generally perform well in the forming section although there are certain limitations. For example, the relatively open weaves, particularly when run at highest speeds, lack dimensional stability. This shortens the overall life of the forming wire which is subject to abrasion as it shifts in position on the machine. In addition, the relatively open weaves are less than fully supportive of the furnish fibers deposited on the wire. Ideally, the fiber and sheet supporting properties of a wire should be increased without significant decrease of water removal through drainage.
With the structured fabrics of the present invention, many of the above-described shortcomings of the prior art are removed. Forming wires constructed according to the invention may be fabricated from an all monofilament fabric which provides an exceptionally smooth surface to contact the paper sheet. A maximum degree of fiber support is achieved. As a result, relatively mark free paper product is obtained, while the desired advantages of an all monofilament wire are retained, i.e. an efficient degree of water drainage. By the invention, the forming side of the fabric may be constructed for maximum accommodation of different grades of formed paper. For example, the forming side plane of the fabric used for making a fine white paper may be made with the elements required for greater fiber support than needed for the manufacture of a coarse brown paper. Thus, the papermaker can accommodate to the grade of paper being made to achieve a quality product under conditions of maximum production efficiency.
In addition, the structure of the fabrics and the wires of the invention is such that a greater dimensional stability is achieved in both the machine and cross-machine directions. This reduces yarn abrasion and increases operating life of the wire. The overall operating life of the forming wire is significantly increased over prior art wires.
It will be appreciated that there is an extensive range of prior art descriptions in the field of papermaker's fabric. Representative of such descriptions are those found in U.S. Pat. Nos. 3,858,623 to Lefkowitz; 4,182,381 to Gisbourne; 4,359,069 to Hahn; and 4,423,755 to Thompson.